1. Field of the Invention
The present invention relates to an image coding apparatus, an image coding method, and an image coding program that allow for the encoding of images using motion compensation prediction and to an image decoding apparatus, an image decoding method, and an image decoding program that allow for the decoding of images using motion compensation prediction.
2. Description of the Related Art
As a representative example of a video compression coding method, the MPEG series standard is used. In the MPEG series standard, motion compensation is used where a frame is divided into a plurality of blocks and motion from another frame is predicted. In MPEG-4 and AVC/H.264, a mechanism is introduced where the best size among a plurality of motion compensation block sizes is interchangeably used.
In motion compensation prediction in units of blocks, a method for compensating parallel translation between a target block and a reference block is generally used. In addition, a method for compensating transformation of blocks (e.g., enlargement, reduction, and rotation) is under consideration. For example, in Patent document 1, prediction efficiency is improved by adaptively switching between a mode for obtaining a prediction image by parallel translation and a mode for obtaining a prediction image by geometric transformation as an image coding method in which inter-frame prediction is used. It is stated that a motion vector of parallel translation and a motion vector of a lattice point (i.e., a motion vector used in geometric transformation) are coded in this method.    [Patent document 1] JP H8-65680
Under these circumstances, the inventors of the present invention have found a technique for further compressing the entire coding amount by compressing motion vector information using an image coding method in which motion compensation prediction by geometric transformation is used.